1. Field of the Invention
The present invention relates to color printing, and more particularly, to color map conversion between different print modes for color printing.
2. Background
A color map is a table that defines the relationship between different sets of colors, for example, between red, green and blue, commonly abbreviated as RGB, and black, cyan, magenta and yellow, commonly abbreviated as KCMY, for a given print mode, such as a plain paper fine mode or a photo normal mode. The RGB are primary colors from which other colors can be created as a combination thereof. KCMY are the ink colors of pens implemented in conventional Hewlett-Packard color printers. A typical color map is a multi-dimensional table of output color values of KCMY that are indexed by input color values of RGB, represented by a three-dimensional color space, wherein R is a first axis, G is a second axis and B is a third axis. Color maps are used to translate the primary colors of RGB sent by a computer to a printer into the colors of the printer inks, such as KCMY in a typical Hewlett-Packard color printer.
A wide variety of color maps have been developed for color printers including color inkjet printers for printing various types of color images including viewgraphs and photographs. Conventional schemes have been developed for creating color maps for different print modes and different types of print media supported by a particular model of color printer using a complex process involving ink separation, measurement and gamut mapping. Traditionally, unique color maps are created to achieve acceptable color reproduction for every print mode and print media combination supported by a color printer. Prototyping through final development of each color map may take a cumulative effort of several weeks. Creating color maps using these conventional schemes typically require significant amounts of time, labor and hardware resources.
Furthermore, color maps may be inconsistent in different print modes. In some coarse print modes, such as a typical draft print mode, a significant amount of banding and granulation may occur such that the output cannot be reliably measured for a conventional gamut mapping process. Conventional schemes of creating color maps may cause color variations that may occur when characteristics of different drawing pens are taken into account when computing these color maps.
In accordance with one embodiment of the present invention, a method of converting a source color map from a source print mode to a destination print mode is provided. The method includes the steps of: (a) performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; and (b) performing a channel independent clipping process to preserve ink volume and saturation.
Another embodiment of the present invention contemplates a method of converting a source color map from a fine source print mode, with a relatively high resolution, to a coarse destination print mode with a relatively low resolution. This method includes: (a) performing a channel independent clipping process to preserve ink volume and saturation; (b) performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; and (c) parametrically adjusting the constant hue clipping process and the channel independent clipping process to generate a parameterized scale factor.
Another method according to the invention described herein may contemplate converting a source color map from a fine source print mode, with a relatively high resolution, to a coarse destination print mode with a relatively low resolution. This method includes: (a) providing a first conversion table mapping indexed color values of black, cyan, magenta and yellow (KCMY) to ink volumes in the source fine print mode; (b) providing a second conversion table mapping ink volumes of KCMY to indexed color values in the destination coarse print mode; (c) converting input color values of KCMY to ink volumes in the source fine print mode; (d) scaling down the ink volumes of KCMY in the source fine print mode; (e) performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; (f) performing a channel independent clipping process to preserve ink volume and saturation; and (g) converting ink volumes of KCMY to indexed color values in the destination coarse print mode.
In a further embodiment of the present invention, a system is provided for converting a source color map from a source print mode to a destination print mode, comprising: a component for performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; and a component for performing a channel independent clipping process to preserve ink volume and saturation.
In a further embodiment of the present invention, a system is provided for converting a source color map from a fine source print mode with a relatively high resolution to a coarse destination print mode with a relatively low resolution, comprising: a component for performing a channel independent clipping process to preserve ink volume and saturation; a component for performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; and a component for parametrically adjusting the constant hue clipping process and the channel independent clipping process to generate a parameterized scale factor.
In a further embodiment of the present invention, a program product is provided for converting a source color map from a source print mode to a destination print mode, comprising machine-readable program code for causing a machine to perform the following method steps: performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; and performing a channel independent clipping process to preserve ink volume and saturation.
In a further embodiment of the present invention, a program product is provided for converting a source color map from a fine source print mode with a relatively high resolution to a coarse destination print mode with a relatively low resolution, comprising machine-readable program code for causing a machine to perform the following method steps: performing a channel independent clipping process to preserve ink volume and saturation; performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; and parametrically adjusting the constant hue clipping process and the channel independent clipping process to generate a parameterized scale factor.
In a further embodiment of the present invention, a program product is provided for converting a source color map from a fine source print mode with a relatively high resolution to a coarse destination print mode with a relatively low resolution, comprising machine-readable program code for causing a machine to perform the following method steps: providing a first conversion table mapping indexed color values of black, cyan, magenta and yellow (KCMY) to ink volumes in the source fine print mode; providing a second conversion table mapping ink volumes of KCMY to indexed color values in the destination coarse print mode; converting input color values of KCMY to ink volumes in the source fine print mode; scaling down the ink volumes of KCMY in the source fine print mode; performing a constant hue clipping process to preserve ink ratios of destination colors to source colors; performing a channel independent clipping process to preserve ink volume and saturation; and converting ink volumes of KCMY to indexed color values in the destination coarse print mode.